1. Field of the Invention
This invention relates to a frangible projectile, and in particular to a frangible projectile having a cannelure. The invention also relates to a method of canneluring a frangible projectile.
2. Description of Related Art
The Cartridge Collector's Glossary-Illustrated, published by International Ammunition Association, 2001, and made available on their website, defines a “cannelure” as “the circumferential swaged, machined or milled groove(s) around a bullet (for sealing; also often for identification) to a cartridge case.” The cannelure is used, for example, as a guide during crimping of a small arms cartridge to the bullet, and/or for retaining a lubricant. While bullets can be secured to cartridges without using cannelures, cannelures are preferred in many cases because they provide a more secure, accurate, and efficient way of attaching the cartridge to the projectile.
A variety of conventional bullets or other projectiles including cannelures are disclosed in U.S. Pat. Nos. 5,259,320; 5,275,108; 5,105,514; 5,079,986; 4,811,666; 4,517,897; 4,336,756; 2,409,307; 1,944,884; and 326,231.
While canneluring is well-known in the context of conventional projectiles, it has heretofore been impractical to provide cannelures in frangible projectiles, which are designed to break apart upon impact, rather than penetrating the target. Conventional machining or milling techniques tend to fracture or weaken the projectile, which is typically made of a compressed powder rather than solid material.
Frangible projectiles are generally lighter than conventional projectiles, and are often used as practice rounds on firing ranges or in situations where non-lethal force is required. To achieve disintegration, frangible projectiles are conventionally made of powdered and compressed materials, rather than solid metal. Originally made of lead powders, frangible projectiles have more recently been made of less toxic materials such as compressed copper and tin powders.
Cannuluring of frangible projectiles is desirable for the same reasons that apply to other types of projectiles, including secure and simple attachment of cartridge shells, identification, and lubrication. Nevertheless, there have only been a few attempts to provide cannelured projectiles, and none has proven practical for mass-market civilian applications. Examples of conventional frangible projectiles that lack cannelures are disclosed in U.S. Published Patent Application Nos. 2003/0101891 and 2001/0050020 and U.S. Pat. No. 6,536,352.
An early attempt at canneluring a frangible projectile is disclosed in U.S. Pat. No. 2,105,528, which is specifically directed to a small arms projectile for use in shooting galleries, including a “grease groove” corresponding to the cannelure of a conventional projectile. However, the method disclosed in this patent can only be used with lead powder mixtures, and is in any case unsuitable for use with modern frangible projectiles, since it involves hardening the projectile before forming the cannelure by crimping or swaging.
Another “frangible” projectile with a cannelure is disclosed in U.S. Pat. No. 5,442,989. The projectile includes a penetrating rod and incendiary component, with the body of the projectile being arranged not only to disintegrate upon contact, but to disintegrate into granules that are propelled outwardly “in every direction with great energy” in order to increase the damage caused by the projectile prior to penetration. The cannelure is used to hold a rotator band or ring for engaging the rifling of a gun barrel, the groove being molded into the body of the projectile prior to sintering. Again, the method disclosed in this patent is not suitable for application to frangible projectiles of the type intended for general use, because it requires hardening of the projectile after molding the groove into the body of the projectile.
There is consequently a long-felt need for a method that enables cannelures to be formed in frangible powdered metal type projectiles intended for general use.